FIBRE ROPES
See the Code of Safe Working Practices Chapter 15 Section 4 and Chapter 16 Section 2.
CONSTRUCTION
Fibre ropes are made from fibres of varying length
depending on their source. these are twisted up
into yarns, and the twist given binds the fibres firmly
together so that they hold by friction when the yarn is
subjected to strain. The yarns are then laid up to form
rope.
As the rope is laid up its length contracts like a coiled spring giving it a certain elasticity, the harder the twist given to the strands the shorter will be the resulting rope.
LAY
Most ropes are laid up right handed, that is the
strands twist away from the eye in a right handed spiral.
In a normal right hand laid rope the fibres are spun right handed to form yarns, the yarns are twisted left handed into strands and the strands right handed into rope. A three stranded rope constructed this way is known as right hand hawser laid rope.
Ropes can be constructed in other patterns:
Left Hand Lay - rarely used at sea.
Shroud Laid - rarely used.
Cable Laid - rarely used.
Braided - Constructed by crossing and recrossing the strands in "Maypole" fashion so that each passes alternately over and under one of the others to form a circular rope.
Braid on Braid - This has a braided core surrounded by a braided sheath. The rope is balanced to that the load is shared equally between the core and the sheath. This construction has the following advantages over hawser laid rope; good flexibility, easy handling wet or dry, non-rotating, non-kinking, even sheath wear. Regardless of wear or damage to the sheath the core will still retain its original strength.
Plaited Rope - Constructed of eight strands arranged in four pairs. Two of left hand lay and two of right hand lay. This construction is also known as Squareline or Multi-plait.
Small Stuff
All cordage under 4mm diameter in size is called "small stuff". This includes twines, spunyarn and marline.
Seaming Twine - a three ply hemp.
Used for sewing canvas and whippings.
Spunyarn - tarred three ply hemp used for servings and
seizings.
Marline - tarred two ply hemp used for serving wire rope
and seizings.
These are the natural fibre types. Various types of man made fibre cordage are available to do similar jobs.
MATERIALS USED AND CHARACTERISTICS
Natural Fibres
Manila: made from the leaf fibre of the "Abaca" plant which is grown in the Philippines. When new and untreated it is a deep golden brown in colour. The rope is flexible, durable, strong and stands up well to wear, weather and salt water.
Sisal: made from the leaves of the "Agaue Sisalana" plant grown in Southern Africa and South America. When new and untreated it is hairy, and a pale straw colour. It is as strong as manila but not as flexible, durable or resistant to wear and weather.
Natural fibre ropes are treated with a fungicide to prevent rot. When wet these ropes will shrink in length and swell in diameter. They must never be stowed away wet.
Man Made Fibres (Synthetic Fibres)
Polyamide: commonly known as Nylon and made from coal. It is resistant to alkalis and mineral oils but is attacked by acids, bleaching agents and paint removers.
Polyester: commonly known as Terylene, made from petroleum. It is resistant to acids, mineral oils and paint removers but is attacked by alkalis.
Polyethylene: made from petroleum. It is resistant to acids, alkalis, mineral oils and bleaching agents but it is attacked by some solvents.
Polypropylene: often referred to as polyprop. It is resistant to acids, alkalis and mineral oils. May be attacked by some solvents. It will float indefinitely. Read M 698.
It is made from four types of fibres.
1. Multi filament - Very fine continuous fibres of circular cross sections less than 50 microns (0.002 inches) in diameter.
2. Mono filament - Coarser fibres continuous in length of circular cross section, larger than 50 microns.
3. Staple spun - Discontinuous fibres produced from either multi or mono filament fibres cut into discrete lengths. This is the commonest type for general marine ropes.
4. Fibre film - Extruded tape which is orientated by heat treatment.
All man made fibres are rot proof, they are considered to be non-flammable in that they do not readily ignite or burn with a flame.
COMPARISON TABLES
Specific gravities
Polyamide
1.14
Polyester
1.38
Polyethylene
0.95 - 0.96
Polypropylene 0.91
Manila and sisal
1.5
Melting points
Polyamide
250°C
Polyester
260°C
Polyethylene
135 °C
Polypropylene 165
°C
Manila and
sisal
Do not melt, but charring commences at 150°C.
A comparison of 48mm diameter ropes taking Manila (grade) 1 = 100 per cent.
Weight
Breaking
Comparison Load Comparison
Manila grade 1
100
100
Sisal and Manila grade 2
100
88
Polyamide
93.5
250
Polyester
115
200
Polyethylene
71
135
Polypropylene
65
167
Elasticity (extension before parting)
Polyamide
50%
Polyester
36%
Polyethylene
33%
Polypropylene
44%
Identification
Polyamide - Soft and silky - One green yarn is one strand.
Polyester - Soft and silky - One blue yarn in one strand.
Polyethylene - Wiry like bristles - One orange yarn in one strand or all orange.
Polypropylene - Multi filament - Soft and silky )one
Mono filament - Wiry like bristles ) yarn
Staple spun - Soft like animal hair ) in one
Fibre film - Harsh like straw ) or all brown
INSPECTION AND MAINTENANCE
1.Before use a rope should be examined visually throughout its length and its residual strength assessed. The latter can be carried out fairly accurately by assessing the external damage as a percentage of the cross-sectional area of the rope.
Always assess the strength in the worst worn or damaged parts of the rope, and bear in mind that man-made fibres do not deteriorate in strength be wetting and drying as do natural fibres.
Cut out any particularly badly worn or damaged parts and splice-up.
A rope is not progressively weakened by an increased number of splices; the approximate 10% reduction in rope strength at a splice is equally effective if one, or more splices, are in a rope.
2.In addition to external wear, inspect also for wear between the strands. In excessive cases a high degree of powdering will be visible, giving a clear indication that the rope has been worked hard, and that its strength is impaired to some degree in addition to the loss caused by external wear as outlined above. Materials with high stretch will show greater interstrand wear and powdering than those that do not stretch so much. As an indicator of extreme overworking some ropes (polyamide (nylon) in particular) may become hard and stiff.
3.The effect of chemical contamination of ropes depends to a great extent on the type of fibre from which the rope is made.
Polyamide (nylon) will be attacked by moderate concentration of acids, whilst they are virtually immune to damage by alkalis.
Polyester rope is the reverse of polyamide (nylon) being highly resistant to acids and will be damaged by alkalis, whilst polypropylene ropes are unaffected by either acids or alkalis.
All types of man-made fibres are attacked to a greater or lesser degree by organic solvents, such as white spirit, xylene and metacresol. Avoid rope contact with wet paint or coal tar and paint stripping preparations.
To be safe wash any rope thoroughly with water as soon as possible should it become contaminated either with acids, or alkalis or solvents.
4.Where
thimbles are fitted to man-made fibre ropes, ensure by
inspection that they have not become slack in the rope
eye. If excessive slackness exists, tighten the rope eye
around the thimble by seizing at the throat with strong
man-made fibre cord, at the same time ensuring that the
thimble itself is not badly distorted or damaged.
The strength of fibre ropes may be assessed using the following formulae where D is the diameter in millimetres.
Breaking strength
Manila
=
2D2/300 tonnes
Polyethylene =
3D2/300
tonnes
Polypropylene =
3D2/300
tonnes
Polyester =
4D2/300
tonnes
Polyamide =
5D2/300
tonnes
The Safe working Load (SWL) is found by allowing a safety
factor of six for general marine work. i.e. SWL =
Breaking Strength/6
CARE AND SAFETY PRECAUTIONS
1.When taking new ropes out of the coil always do so in an anticlockwise direction to avoid disturbing the lay of the rope. If the coil can be suspended on a swivel, rotated, and the rope taken from outside the coil, "turns' in the rope will be avoided.
2.Do not surge ropes on winch barrels if it can be avoided. Do not pay out or slack away by rendering, but always try to walk back the rope.
3.See that the surface condition of winch barrels is good, and that they are free from rust and paint.
4.Do not use more than three turns of the rope on the winch barrel.
5.On whelped drums, it is suggested that one or two extra turns be made to ensure a good grip. A whelped drum is one which has ridges on its surface.
6.See that fairleads are in good condition and if of the roller type, ensure that they rotate properly and are lubricated regularly.
7.Avoid sharp angles in the rope.
8.It is advisable to use man-made fibre rope stoppers on man-made fibre mooring lines.
9.It is important when Joining wire rope to any man-made (or natural) fibre rope that a thimble be inserted in the eye of the fibre portion, and at all times both ropes should have the same direction of lay.
10. Do not leave ropes unduly exposed to sunlight when at sea; keep covered by tarpaulins, or store below deck.
11. Keep ropes clear of contamination by chemicals.
12. Do not store ropes in the vicinity of boilers or heaters.
13. Have as few men as possible in the vicinity of all ropes under strain particularly man-made fibre ropes and wire ropes.
14. Never stand in the bight of a rope or in the path of a rope under strain.
15. Ensure that all splices are intact as all the tucks recommended by the ropemakers are necessary for safety.
16. Never allow a wire rope to cross a fibre rope on a bollard.
17. Always make certain that the end of a man-made fibre rope is made fast to bitts
And not just wound on the drum end.
18. Man-made fibre ropes, unlike natural fibre ropes, when approaching the breaking point give no audible or visual warning. Stretch imparted to man-made fibre ropes is recovered almost instantaneously with release of tension and with considerable recoil if fracture of the rope occurs. Polypropylene rope, however, has less recoil effect than either polyamide or polyester.